Punching reinforcement size vs. capacity

How come a smaller reinforcement area can be ok, but not when an increase in reinforcement bar diameter is not?


An edge column with ø6s150, result is OK!



Same column, same forces, but with ø10s150, the result is no longer OK!



The reason is that the stresses are slightly increased with ø10 compared to ø6 since the effective height d is being reduced.

The stress is calculated as vEd = beta * VEd / (u0 * d). Normally the capacity is increased with increased reinforcement, but in this case the minimum value vmin is the designing factor: EN 1992-1-1 (6.47).


If the reinforcement is increased the capacity will at some point increase too since it will be dependant on the actual reinforcement. It has a upper value of what can be utilized ra <= 0.02, though.

J
Joakim is the author of this solution article.

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